The present invention relates to a method and apparatus for machining cavities and slots in an electrode workpiece by electrical discharge machining by means of an electrode tool, wherein each electrode is displaced in a predetermined direction at an appropriate rate by way of its own servo-motor feed mechanism.
It is known, in EDM technology, to displace the electrodes in different directions, for example for cutting a workpiece according to a programmed path by means of a wire electrode. It is also known to control the displacement of the electrode tool in the same predetermined direction by means of two servo-motors, one providing rapid feed of the electrode tool and having a limited travel, and the second providing slow feed but having a substantial travel, the displacement effected by the second servo-motor being controlled as a function of the displacement controlled by the first motor. Such an arrangement is disclosed in U.S. Pat. No. 3,758,739.
Another known EDM process utilizing one or two servo-motors consists in relatively displacing the electrodes according to a translation motion following either a linear path different from the axis of feed of the electrode tool into the electrode workpiece, or a path inscribed on a surface of revolution of increasing cross-section in the direction of the axis of penetration of the electrode tool into the electrode workpiece. Such an arrangement, using a single servo-motor is disclosed in German Patent publication No. 2,238,698 and Swiss patent No. 588,917 and the corresponding application in the United States, Ser. No. 696,713, filed June 16, 1976 now U.S. Pat. No. 4,104,501, assigned to the same assignee as the present application.
The present invention relates to a method and apparatus permitting to form by EDM cavities and slots in an electrode workpiece by displacing the electrode tool and the electrode workpiece relative to each other according to a translation motion along a predetermined path, such relative displacement being controlled on the one hand such as to maintain predetermined machining conditions in the machining zone beween the electrodes, and on the other hand such as to cause the relative position of the electrodes to reach a value at most equal to a predetermined limit value.